1. C++ Data Types and Data Abstractions

2. C++ Data Types Namespaces Built-in data types Literal constants
Variables
Pointers
References
The C++ string Type
The const Qualifier

3. What is “using namespace std;”
#include <iostream>
using namespace std;
void main ( ) {
int start = 5;
int end = 19;
if (start < end ) {
cout << “A”;
} // end if
cout << “B”;
} // end main

4. Namespaces
The problem: When two variables (or functions) in global scope have the same identifier (name), we get a compile-time error.
To avoid such name collisions, programmers need to use unique identifiers in their own code.
In C, if you use multiple third-party libraries and there is a name collision, you have three choices:
Get the source code to the libraries and modify and recompile it,
ask one of the library publishers to rename their identifiers, or
decide not to use one of the libraries.
Often, none of these options are available.

5. Namespaces To tackle this problem, C++ introduced namespaces.
All identifiers declared within a defined block are associated with the block’s namespace identifier.
All references to these identifiers from outside the block must indicate the namespace identifier.
One example is the namespace std, in which Standard C++ defines its library’s identifiers, such as the cout stream object.

6. Namespaces
You can access objects in the namespace std in the following way using the scope resolution operator “::”
#include <iostream>
int main() {
std::cout << “Hello World!”;
return 0; }

7. Namespaces
Or, you can use the using namespace statement to omit the corresponding namespace references:
#include <iostream>
using namespace std;
int main() {
cout << “Hello World!”;
return 0; }

8. Namespaces This is how you define your own namespaces:
#include <iostream>
namespace MyNames {
int value1 = 10;
int value2 = 20;
int ComputeSum()
return (value1 + value2); }
int main()
std::cout << MyNames::ComputeSum() << std::endl;

9. Namespaces
If you use multiple using namespace statements, you may get a compile-time error due to ambiguity:
#include <iostream>
namespace MyNames {
int value1 = 10;
int value2 = 20; }
namespace MyOtherNames
int value1 = 30;
int value2 = 40;
using namespace std;
using namespace MyNames;
using namespace MyOtherNames;
int main() {
value1 = 50; }

10. Namespaces You can also define nested namespaces:
#include <iostream>
namespace MyNames {
int value1 = 10;
int value2 = 20;
namespace MyInnerNames
int value3 = 30; }
int main()
std::cout << MyNames::value1 << std::endl;
std::cout << MyNames::MyInnerNames::value3 << std::endl;

11. Numeric Data Types
Type char represents individual characters and small integers (1 byte).
Types short, int, and long represent integer values (half a machine word, 1 machine word, 1 or more machine words)
Types float, double, and long double represent floating point values (1 machine word, 2 machine words, 3 or 4 machine words)

12. Numeric Data Types
Type char, short, int, and long are also called integral types.
Integral types can be signed or unsigned.
Example: The value of an 8-bit unsigned char ranges from 0 to 255, while the range for an 8-bit signed char is from –128 to 127.

13. Literal Constants
Literal constants are values that occur in a program.
Example:
int main() {
int students = 21;
double pi = ; }
Here, 21 is a literal constant of type int, and is a literal constant of type double.

14. Literal Constants
We can use prefixes to write literal integer constants in decimal, octal, or hexadecimal notation.
Examples: Decimal (no prefix): 15
Octal (prefix 0 [zero]): 015
= 13 (decimal)
Hexadecimal (prefix 0x [zero-x]): 0x15
= 21 (decimal)

15. Literal Constants
By default, the C++ compiler assumes that all literal integer constants are of type int and all literal floating point constants are of type double.
You can specify different types by appending a letter to the literal integer constant.
Examples:
2344U (unsigned)
1555L (long)
166UL (unsigned long)
3.1416F (float)
6.2831L (long double)

16. Literal Constants
Another built-in (or primitive) C++ data type is the type bool.
Its only literals are true and false.
Note that the type bool does not exist in C.
In C, we represent the Boolean values true and false by the integers 1 and 0.

17. Literal Constants
We use single quotation marks to write literal character constants.
Examples: ‘x’, ‘4’, ‘:’, ‘ ‘ (space)
Nonprintable characters and some special characters can be represented by escape sequences.
Examples:
‘\n’ (newline), ‘\a’ (bell), ‘\t’ (tab)
‘\\’ (backslash), ‘\’’ (single quote), ‘\”’ (double quote)

18. Literal Constants
Generalized escape sequences are indicated by a backslash followed by up to three digits.
The value of the digits in the sequence is interpreted as the corresponding literal constant in the ASCII character set.
Examples:
\7 (bell)
\14 (newline)
\65 (‘5’)

19. Literal Constants
A character literal can be preceded by an L, for example: L’a’
This is called a wide-character literal and has type wchar_t.
Such wide-character literals support language character sets like Chinese and Japanese, which cannot be represented within the 256 character ASCII set.

20. Literal Constants
A literal string constant is composed of zero or more characters enclosed in double quotation marks.
Examples:
“” (null string)
“x”
“hello”
“Hi,\nHow are you?\n”

21. Literal Constants
A string literal can be written across multiple lines. You can use a backslash as the last character on a line to indicate that the string continues on the next line.
Example:
“This is an \
excellent \
multi-line string literal.”

22. Variables write to, read from, and manipulate
Variables provide us with named memory storage that we can
write to,
read from, and
manipulate
throughout the course of our program.
Each variable has a specific type, which determines
the size and layout of its associated memory,
the range of values that can be stored, and
the set of operations that can be applied to it.
Variables are also referred to as objects.

23. Variables There are two values associated with a variable:
Its data value, which is stored at some memory address. It is also called the rvalue (read value) of the variable.
Its address value, indicating the location in memory where its data value is stored. This value is also referred to as the variable’s lvalue (location value).

24. Pointers A pointer holds the memory address of another object.
Through the pointer we can indirectly manipulate the referenced object.
Pointers are useful for
Creating linked data structures such as trees and lists,
management of dynamically allocated objects, and
as a function parameter type for passing large objects such as arrays.

25. Pointers Every pointer has an associated type.
The type of a pointer tells the compiler how to interpret the memory content at the referenced location and how many bytes this interpretation includes.
Examples of pointer definitions:
int *pointer;
int *pointer1, *pointer2;
string *myString;

26. Pointers
The dereference operator (*) dereferences a pointer variable so that we can manipulate the memory content at the location specified by the pointer.
The address-of operator (&) provides the memory address (a pointer) of a given object.

27. Pointers Example: Correct or incorrect?
int var1=333, var2=444, *pvar1, *pvar2;
pvar1 = var1;
incorrect. *int  int
pvar2 = &var2;
correct. *int = *int
*pvar1 = var2;
correct. int = int
*pvar2 = *pvar ;
correct. int = int

28. Pointers
Notice that in pointer definitions the ‘*’ symbol indicates the pointer type and is not the dereference operator.
Example:
int var;
int *pvar1 = var;
Incorrect! During initialization a pointer can only be assigned an address:
int *pvar1 = &var;
Correct!

29. References
References (aliases) can be used as alternative names for objects.
In most cases they are used as formal parameters to a function.
A reference type is defined by following the type specifier with the address-of operator.
Example:
int val1 = 333;
int &refVal1 = val1;

30. References A reference must be initialized.
Once defined, a reference cannot be made to refer to another object.
All operations on the reference are actually applied to the object to which the reference refers.
Example:
int val1 = 333;
int &refVal1 = val1;
val1++;
refVal1 += 100;
cout << “Result: ” << refVal1;
Result: 434

31. Pass-by-value sends a copy of the contents of the actual parameter
CALLING
BLOCK
FUNCTION CALLED
SO,
the actual parameter cannot be changed by the function. 31

32. Pass-by-reference sends the location (memory address)
of the actual parameter
CALLING
BLOCK
FUNCTION CALLED
can change value of
actual parameter 32

33. The C++ string Type
To use the C++ string type, you must include its associated header file:
#include <string>
Different ways to initialize strings:
string myString(“Hello folks!”);
string myOtherString(myString);
string myFinalString; // empty string
The length of a string is returned by its size() operation (without the terminating null character): cout << myString.size();
= 12

34. The C++ string Type
We can use the empty() operation to find out whether a string is empty:
bool isStringEmpty = myString.empty();
Use the equality operator to check whether two strings are equal:
if (myString == myOtherString)
cout << “Wow, the strings are equal.”;
Copy one string to another with the assignment operator: myFinalString = myOtherString;

35. The C++ string Type Use the plus operator to concatenate strings:
string s1 = “Wow! ”, s2 = “Ouch! ”;
const char *s3 = “Yuck! ”
s2 += s1 + s3 + s2;
cout << s2;
= Ouch! Wow! Yuck! Ouch!

36. The const Qualifier
The const type qualifier transforms an object into a constant. Example: const double pi = ;
Constants allow you to store parameters in well- defined places in your code
Constants have an associated type.
Constants must be initialized.
Constants cannot be modified after their definition.
Constants replace the #define “technique” in C.

37. The const Qualifier
Sometimes you may want to define for your object a set of states or actions.
For example, you could define the following states for the Student Counselor:
observeStudent
shoutAtStudent
followStudent
rechargeBattery

38. The const Qualifier
Using the const qualifier, you could define the following constants:
const int observeStudent = 1;
const int shoutAtStudent = 2;
const int followStudent = 3;
const int rechargeBattery = 4;
A function SetRobotState could then be defined as follows:
bool SetRobotState(int newState) { …
int currentState = newState;
return executionSuccessful; }

39. Enumeration Types
However, mapping states onto integers has certain disadvantages:
You cannot restrain the range of values that are passed to SetRobotState.
There is no useful typing – if you define individual sets of states for multiple objects, each object could formally be set to any of these states, not only its individual ones.
This problem can be solved with enumeration types.

40. Enumeration Types Enumeration types can be defined as follows:
enum robotState { observeStudent = 1, shoutAtStudent,
followStudent,
rechargeBattery };
This way we defined a new type robotState that can only assume four different values.
These values still correspond to integers. For example,
cout << followStudent;
gives you the output ‘3’.

41. Enumeration Types
We are now able to restrain the values that are passed to SetRobotState to the four legal ones:
bool SetRobotState(robotState newState) { …
robotState currentState = newState;
return executionSuccessful; }
Any attempt to call SetRobotState with an integer value or a value of a different enumeration type will cause an error at compile time.

42. C++ Data Types simple structured address integral enum floating
float double long double
array struct union class
char short int long bool
address
pointer reference

43. Structured Data Types
Chapter 11

44. C++ Data Types simple structured address integral enum floating
Skipping for now…
integral enum
floating
float double long double
array struct union class
char short int long bool
address
pointer reference

45. Structured Data Type
A structured data type is a type in which each value is a collection of component items.
The entire collection has a single name each component can be accessed individually

46. C++ Structured Type
Often we have related information of various types that we’d like to store together for convenient access under the same identifier, for example . . .

47. thisAnimal .id 2037581 .name “giant panda” .genus “Ailuropoda”
.species “melanoluka”
.country “China”
.age
.weight
.health Good

48. anotherAnimal .id 5281003 .name “llama” .genus “Lama”
.species “peruana”
.country “Peru”
.age
.weight
.health Excellent

49. struct AnimalType enum HealthType { Poor, Fair, Good, Excellent } ;
struct AnimalType // declares a struct data type
{ // does not allocate memory
long id ;
string name ;
string genus ;
string species ; struct members
string country ;
int age ;
float weight ;
HealthType health ;
} ;
AnimalType thisAnimal ; // declare variables of AnimalType
AnimalType anotherAnimal ; 49

50. struct type Declaration
SYNTAX
struct TypeName {
MemberList
} ;
MemberList SYNTAX
DataType MemberName ; .

51. struct type Declaration
The struct declaration names a type and names the members of the struct.
It does not allocate memory for any variables of that type!
You still need to declare your struct variables.

52. struct type declarations
If the struct type declaration precedes all functions it will be visible throughout the rest of the file. If it is placed within a function, only that function can use it.
It is common to place struct type declarations with TypeNames in a (.h) header file and #include that file.
It is possible for members of different struct types to have the same identifiers. Also a non-struct variable may have the same identifier as a structure member.

53. Accessing struct Members
Dot ( period ) is the member selection operator.
After the struct type declaration, the various members can be used in your program only when they are preceded by a struct variable name and a dot.
EXAMPLES
thisAnimal.weight
anotherAnimal.country

54. Valid operations on a struct member depend only on its type
thisAnimal.age = 18;
thisAnimal.id = ;
cin >> thisAnimal.weight;
getline ( cin, thisAnimal.species );
thisAnimal.name = “giant panda”;
thisAnimal.genus[ 0 ] = toupper (thisAnimal.genus[ 0 ] ) ;
thisAnimal.age++;

55. Aggregate Operation
An Aggregate operation is an operation on a data structure as a whole, as opposed to an operation on an individual component of the data structure.

56. Aggregate struct Operations
I/O, arithmetic, and comparisons of entire struct variables are NOT ALLOWED!
Operations valid on an entire struct type variable:
assignment to another struct variable of same type,
pass to a function as argument (by value or by reference),
return as value of a function

57. Examples of aggregate struct operations
anotherAnimal = thisAnimal ; // assignment
WriteOut(thisAnimal); // value parameter
ChangeWeightAndAge(thisAnimal); // reference parameter
thisAnimal = GetAnimalData( ); // return value of function

58. void WriteOut( /* in */ AnimalType thisAnimal)
// Prints out values of all members of thisAnimal
// Precondition: all members of thisAnimal are assigned
// Postcondition: all members have been written out {
cout << “ID # “ << thisAnimal.id << thisAnimal.name << endl ;
cout << thisAnimal.genus << thisAnimal.species << endl ;
cout << thisAnimal.country << endl ;
cout << thisAnimal.age << “ years “ << endl ;
cout << thisAnimal.weight << “ lbs. “ << endl ;
cout << “General health : “ ;
WriteWord ( thisAnimal.health ) ; } 58

59. Passing a struct Type by Reference
void ChangeAge ( /* inout */ AnimalType& thisAnimal )
// Adds 1 to age
// Precondition: thisAnimal.age is assigned
// Postcondition: thisAnimal.age == + 1 {
thisAnimal.age++ ; }

60. AnimalType GetAnimalData ( void )
// Obtains all information about an animal from keyboard
// Postcondition:
// Function value == AnimalType members entered at kbd {
AnimalType thisAnimal ;
char response ;
do { // have user enter all members until they are correct .
} while (response != ‘Y’ ) ;
return thisAnimal ; } 60

61. Hierarchical Structures
The type of a struct member can be another struct type. This is called nested or hierarchical structures.
Hierarchical structures are very useful when there is much detailed information in each record.
FOR EXAMPLE . . .

62. struct MachineRec Information about each machine in a shop contains:
an idNumber,
a written description,
the purchase date,
the cost,
and a history (including failure rate, number of days down, and date of last service).

63. struct StatisticsType { float failRate ;
struct DateType
{ int month ; // Assume
int day ; // Assume
int year ; // Assume };
struct StatisticsType
{ float failRate ;
DateType lastServiced ; // DateType is a struct type
int downDays ;
} ;
struct MachineRec
{ int idNumber ;
string description ;
StatisticsType history ; // StatisticsType is a struct type
DateType purchaseDate ;
float cost ;
MachineRec machine ; 63

64. struct type variable machine
5719 “DRILLING…”
.month .day .year
.failrate .lastServiced .downdays
.month .day .year
.idNumber .description . history purchaseDate cost
machine.history.lastServiced.year has value 1999

65. C++ Data Types simple structured address integral enum floating
float double long double
array struct union class
char short int long bool
address
pointer reference

66. Unions in C++ Definition For Example
A union is a struct that holds only one of its members at a time during program execution.
For Example
union WeightType {
long wtInOunces ;
int wtInPounds; only one at a time
float wtInTons;
} ;

67. Using Unions union WeightType // declares a union type {
long wtInOunces ;
int wtInPounds;
float wtInTons;
} ;
WeightType weight; // declares a union variable
weight.wtInTons = 4.83 ;
// Weight in tons is no longer needed. Reuse the memory space.
weight.wtInPounds = 35;

68. Abstraction
Abstraction is the separation of the essential qualities of an object from the details of how it works or is composed
It focuses on what, not how
It is necessary for managing large, complex software projects

69. Control Abstraction
Separates the logical properties of an action from its implementation .
Search (list, item, length, where, found);
The function call depends on the function’s specification (description), not its implementation (algorithm)

70. Data Abstraction
Separates the logical properties of a data type from its implementation
LOGICAL PROPERTIES IMPLEMENTATION
What are the possible values? How can this be done in C++?
What operations will be needed? How can data types be used?

71. Data Type set of values allowable operations (domain) on those values
For example, data type int has
domain
operations
+, -, *, /, %, >>, <<

72. Abstract Data Type (ADT)
Is a programmer-defined type with a set of
values and allowable operations for the type.
Some ways to define a new C++ type are:
using typedef
using struct
using class

73. Using typedef typedef int Boolean; typedef char String20 [21] ;
String20 message; // variable declarations
Boolean seniorCitizen;

74. Using struct typedef char String20 [ 21 ] ;
struct EmployeeType { // declares a struct data type
long idNumber ;
String20 name ; data members
int hoursWorked ;
int numDependents ;
float hourlyWage ;
} ;
EmployeeType mySelf; // declares variable

75. mySelf
.idNumber
.name ‘B’ ‘a’ ‘r’ ‘b’ ‘a’ ‘r‘ ‘a’ ‘ ’ ‘ ’ ‘ ’ ‘ ’ ‘\0’
.hoursWorked
.dependents
.hourlyWage

76. Abstract Data Type (ADT)
An ADT is a data type whose properties (domain and operations) are specified (what) independently of any particular implementation (how)
For example . . .

77. ADT Specification Example
TYPE
TimeType
DOMAIN
Each TimeType value is a time in hours, minutes, and seconds.
OPERATIONS
Set the time
Print the time
Increment by one second
Compare 2 times for equality
Determine if one time is “less than” another

78. Another ADT Specification
TYPE
ComplexNumberType
DOMAIN
Each value is an ordered pair of real numbers (a, b) representing a + bi.
OPERATIONS
Initialize the complex number
Write the complex number
Add
Subtract
Multiply
Divide
Determine the absolute value of a complex number

79. ADT Implementation means
Choosing a specific data representation for the abstract data using data types that already exist (built-in or programmer-defined)
Writing functions for each allowable operation

80. Information Hiding
Class implementation details are hidden from the client’s view. This is called information hiding.
Public functions of a class provide the interface between the client code and the class objects.
client
code
abstraction
barrier
specification
implementation

81. Benefits of information hiding
Data and details can be concealed from the client of the abstraction.
Code can be changed without affecting the client because the specification and interface are unchanged.

82. Several Possible Representations of TimeType
3 int variables
3 strings
3-element int array
Actual choice of representation depends on time, space, and algorithms needed to implement operations
“10” “45” “27”

83. Some Possible Representations of ComplexNumberType
struct with 2 float members
2-element float array
.real imag

84. C++ Data Types simple structured address integral enum floating
float double long double
array struct union class
char short int long bool
address
pointer reference

85. class TimeType Specification
// Specification File ( timetype.h )
class TimeType // declares a class data type
{ // does not allocate memory
public : // 5 public function members
void Set ( int hours , int mins , int secs ) ;
void Increment ( ) ;
void Write ( ) const ;
bool Equal ( TimeType otherTime ) const ;
bool LessThan ( TimeType otherTime ) const ;
private : // 3 private data members
int hrs ;
int mins ;
int secs ;
} ;

86. Use of C++ data Type class
Facilitates re-use of C++ code for an ADT
Software that uses the class is called a client
Variables of the class type are called class objects or class instances
Client code uses public member functions to handle its class objects

87. Using class
A class is a programmer-defined type whose components (called class members) can be variables or functions.
Class members are private by default. Compiler does not permit client code to access private class members.
Class members declared public form the interface between the client and the class.
In most classes, the private members contain data, and the public members are functions to manipulate that data.

88. Member functions categorized by task
CONSTRUCTOR -- a member function that actually creates a new instance and initialized some or all of its data members
ACCESS FUNCTION or OBSERVER -- a member function that can inspect (use but not modify) the data members of a class without changing their values. Such a function is declared with const following the parameter list in both the specification and the implementation files.

89. Client Code Using TimeType
#include “timetype.h” // includes specification of the class
using namespace std ;
int main ( ) {
TimeType currentTime ; // declares 2 objects of TimeType
TimeType endTime ;
bool done = false ;
currentTime.Set ( 5, 30, 0 ) ;
endTime.Set ( 18, 30, 0 ) ;
while ( ! done ) {
currentTime.Increment ( ) ;
if ( currentTime.Equal ( endTime ) )
done = true ;
} ; } 89

90. class type Declaration
The class declaration creates a data type and names the members of the class.
It does not allocate memory for any variables of that type!
Client code still needs to declare class variables.

91. C++ Data Type class represents an ADT
2 kinds of class members: data members and function members
Class members are private by default
Data members are generally private
Function members are generally declared public
Private class members can be accessed only by the class member functions (and friend functions), not by client code.

92. Aggregate class Operations
Built-in operations valid on class objects are:
Member selection using dot ( . ) operator ,
Assignment to another class variable using ( = ),
Pass to a function as argument
(by value or by reference),
Return as value of a function
Other operations can be defined as class member functions

93. 2 separate files Generally Used for class Type
// Specification File ( timetype .h )
// Specifies the data and function members.
class TimeType {
public:
private:
} ;
// Implementation File ( timetype.cpp )
// Implements the TimeType member functions.

94. Implementation File for TimeType
// Implementation File ( timetype.cpp )
// Implements the TimeType member functions.
#include “ timetype.h” // also must appear in client code
#include <iostream>
bool TimeType :: Equal ( /* in */ TimeType otherTime ) const
// Postcondition:
// Function value == true, if this time equals otherTime
// == false , otherwise {
return ( (hrs == otherTime.hrs) && (mins == otherTime.mins)
&& (secs == otherTime.secs) ) ; }

95. Member selection operator .
When a client uses a public member function, the function call requires a dot preceded by the name of the object. You can think of the function call as being sent to this object.
ofstream outFile ;
outFile.open (“a:\\my.out”) ; .
outFile.close( ) ;
class
type
variable,
object,
instance

96. Familiar Class Instances and Function Members
The member selection operator ( . ) selects either data members or function members
Header files iostream and fstream declare the istream, ostream,and ifstream, ofstream I/O classes
Both cin and cout are class objects and get and ignore are function members
cin.get (someChar) ;
cin.ignore (100, ‘\n’) ;
The statements below, declare myInfile as an instance of class ifstream and invoke function member open
ifstream myInfile ;
myInfile.open ( “A:\\mydata.dat” ) ;

97. Scope Resolution Operator ( :: )
C++ programs typically use several class types
Different classes can have member functions with the same identifier, like Write( )
Member selection operator is used to determine the class whose member function Write( ) is invoked
currentTime .Write( ) ; // class TimeType
numberZ .Write( ) ; // class ComplexNumberType
In the implementation file, the scope resolution operator is used in the heading before the function member’s name to specify its class
void TimeType :: Write ( ) const { }

98. TimeType Class Instance Diagrams
currentTime endTime
Set
Set
Private data:
hrs
mins
secs
Private data:
hrs
mins
secs
Increment
Increment 18 30 17 58 2
Write
Write
LessThan
LessThan
Equal
Equal

99. Use of const with Member Functions
When a member function does not modify the private data members, use const in both the function prototype (in specification file) and the heading of the function definition (in implementation file)

100. Example Using const with a Member Function
void TimeType :: Write ( ) const
// Postcondition: Time has been output in form HH:MM:SS
{ if ( hrs < 10 )
cout << ‘0’ ;
cout << hrs << ‘:’ ;
if ( mins < 10 )
cout << mins << ‘:’ ;
if ( secs < 10 )
cout << secs ; }
100

101. Class Constructors
A class constructor is a member function whose purpose is to initialize the private data members of a class object
The name of a constructor is always the name of the class, and there is no return type for the constructor
A class may have several constructors with different parameter lists. A constructor with no parameters is the default constructor
A constructor is implicitly invoked when a class object is declared--if there are parameters, their values are listed in parentheses in the declaration

102. Specification of TimeType Class Constructors
class TimeType // timetype.h {
public : // 7 function members
void Set ( int hours , int minutes , int seconds ) ;
void Increment ( ) ;
void Write ( ) const ;
bool Equal ( TimeType otherTime ) const ;
bool LessThan ( TimeType otherTime ) const ;
TimeType ( int initHrs , int initMins , int initSecs ) ; // constructor
TimeType ( ) ; // default constructor
private : // 3 data members
int hrs ;
int mins ;
int secs ;
} ;
102

103. Implementation of TimeType Default Constructor
TimeType :: TimeType ( )
// Default Constructor
// Postcondition:
// hrs == 0 && mins == 0 && secs == 0 {
hrs = 0 ;
mins = 0 ;
secs = 0 ; }

104. Implementation of Another TimeType Class Constructor
TimeType :: TimeType ( /* in */ int initHrs,
/* in */ int initMins,
/* in */ int initSecs )
// Constructor
// Precondition: 0 <= initHrs <= && 0 <= initMins <= 59
// <= initSecs <= 59
// Postcondition:
// hrs == initHrs && mins == initMins && secs == initSecs {
hrs = initHrs ;
mins = initMins ;
secs = initSecs ; }
104

105. Automatic invocation of constructors occurs
TimeType departureTime ; // default constructor invoked
TimeType movieTime (19, 30, 0 ) ; // parameterized constructor
departureTime movieTime
Set
Set
Private data:
hrs
mins
secs
Increment
Private data:
hrs
mins
secs
Increment 19 30
Write
Write
LessThan
LessThan
Equal
Equal

106. Separate Compilation and Linking of Files
specification file
main program
timetype.h
implementation file
client.cpp
timetype.cpp
#include “timetype.h”
Compiler
Compiler
client.obj
timetype.obj
Linker
client.exe

107. Avoiding Multiple Inclusion of Header Files
Often several program files use the same header file containing typedef statements, constants, or class type declarations--but, it is a compile-time error to define the same identifier twice
This preprocessor directive syntax is used to avoid the compilation error that would otherwise occur from multiple uses of #include for the same header file
#ifndef Preprocessor_Identifier
#define Preprocessor_Identifier .
#endif

108. Example Using Preprocessor Directive #ifndef
// timetype .h FOR COMPILATION THE CLASS DECLARATION IN
// Specification File FILE timetype.h WILL BE INCLUDED ONLY ONCE
#ifndef TIME_H
#define TIME_H // timetype .cpp // client.cpp
// Implementation File // Appointment program
class TimeType
{ #include “timetype.h” #include “timetype.h”
public:
int main ( void ) {
private: }
} ;
#endif

109. How to create and use them.
The End
Next Lecture
More about classes.
How to create and use them.